Alkyl aromatic polyols, such as alkyl catechols, are useful as antioxidant and friction-modifying additives for lubricating oils. Borated alkyl catechols also find use as lubricating oil additives to reduce engine wear and deposits, thus increasing the useful life of automobile and truck engines.
These alkyl aromatic polyols are typically prepared by alkylating an aromatic polyol with an olefin. Typical olefins used to alkylate aromatic polyols include readily available C.sub.14 to C.sub.28 alpha olefins, polypropylenes and polybutenes. The alkyl group is generally of sufficient carbon number to allow the alkyl aromatic polyol to be soluble in lubricating oil.
The alkylation of aromatic polyols with olefins generally requires a catalyst, such as a Lewis acid or a Bronsted acid. Sulfonic acid resins and polymers, such as Amberlyst-15.RTM., Amberlyst-36.RTM. and Nafion-H.RTM., are frequently used as the catalyst for such reactions, since these materials are insoluble under the reaction conditions and are easily recovered from the reaction mixture by simple filtration.
For example, U.S. Pat. No. 4,632,771, issued Dec. 30, 1986 to T. V. Liston et al., describes the alkylation of catechol with C.sub.14 to C.sub.18 alpha olefins, containing less than 20% C.sub.18 content, using the sulfonic acid resin, Amberlyst-15.RTM., as a catalyst. Similarly, U.S. Pat. No. 4,643,838, issued Feb. 17, 1987 to T. V. Liston et al., describes the alkylation of catechol with C.sub.18 to C.sub.24 olefin mixtures, containing at least 30% branched olefins, using Amberlyst-15.RTM. as a catalyst. The alkyl catechol products of these patents are described as being normally liquid at typical storage temperatures.
Similarly, phenol has been alkylated with alpha olefin oligomers using Amberlyst-15.RTM.. PCT International Publication No. WO 90/07564, published Jul. 12, 1990, discloses liquid alkylphenyl poly(oxypropylene) aminocarbamate fuel and lubricating oil additives and describes the alkylation of phenol with alpha olefin oligomers derived from C.sub.8 to C.sub.20 alpha olefins using Amberlyst-15.RTM. as a catalyst.
Thus, using these previously described procedures, the alkylation of aromatic polyols, such as catechol, with high carbon number alpha olefin oligomers was expected to provide compounds useful for many lubricating oil applications. The unique structure of higher carbon number alpha olefin oligomers was expected to give an aromatic polyol alkylated with such olefins excellent solubility and compatibility in lubricating oils, especially in synthetic or semi-synthetic lubricating oils which consist, at least in part, of hydrogenated alpha olefin oligomers.
Unfortunately, all attempts to alkylate catechol with alpha olefin oligomers derived from C.sub.8 to C.sub.14 alpha olefins using insoluble sulfonic acid catalysts proved unsuccessful. Little or no alkylated products were produced under the normal alkylation reaction conditions even with prolonged reaction times. Thus, a need exists for a new process for alkylating aromatic polyols with high carbon number alpha olefin oligomers.
It has now been found that aromatic polyols can be alkylated with alpha olefin oligomers of alpha olefins having about 8 to 14 carbon atoms using an organic sulfonic acid catalyst, which is soluble under the alkylation reaction conditions, to produce a liquid alkyl aromatic polyol.
Soluble sulfonic acid catalysts have been used previously to alkylate phenol. For example, U.S. Pat. No. 2,865,966, issued Dec. 23, 1958 to B. Y. Abadir, teaches the alkylation of phenol with an acyclic polypropylene in the presence of a hydrate of toluene sulfonic acid.
U.S. Pat. No. 3,932,537, issued Jan. 13, 1976 to W. H. Wetzel et al., teaches the use of either an aryl sulfonic acid having a K value of at least 3.8.times.10.sup.-3 or trifluoromethanesulfonic acid as the catalyst for alkylating a phenol with an alkylating agent consisting of aliphatic olefins having from 2 to about 20 carbon atoms.
U.S. Pat. No. 4,418,222, issued Nov. 29, 1983 to L. R. Honnen, teaches a continuous process for producing para alkyl phenols by reacting phenol with polypropylene in the presence of trifluoromethanesulfonic acid.
These patents, however, do not teach the alkylation of an aromatic polyol, such as catechol, with higher carbon number alpha olefin oligomers.